This application claims priority from German Patent Application No. 198 25 080.0, filed Jun. 4, 1998.
The present invention relates to a method of producing foil bags, wherein two foils are supplied to form the side walls of the foil bag and a bottom foil is supplied to form the bottom of the foil bag, and the foils are interconnected, and to an apparatus for carrying out the method.
Foil bags are used for receiving filling material, such as beverages. Such foil bags consist e.g. of two side foils which are sealed to each other at two opposite edges. A bottom foil which in the folded-apart state constitutes a standing base and forms a space for the filling material between the side foils is sealed in between the corresponding third edges. After the filling operation the four side edges are sealed to one another.
For the manufacture of such foil bags the side foils and the bottom foil are unwound in one piece from corresponding supply rolls in automated processing lines, placed one upon the other in the correct layer sequence and then, as described above, sealed to one another. The resulting row of foil bags is then cut along the weld seams into individual foil bags.
It must be guaranteed that the side foils are also interconnected in the area of the bottom foil to ensure a stable foil bag. To this end, corresponding recesses must be provided in the bottom foil so as to ensure that the side edges of the side foils are also interconnected in the area of the bottom foil.
Due to a malfunction it may easily happen that the recesses are defective, displaced or not produced at all. Since the bottom foil comes to rest between the two side foils and is thus not visible in the unfilled state of the foil bag, a visual inspection for checking wether the bottom foil comprises corresponding recesses can only be carried out under great efforts with the further processing operation being slowed down or interrupted.
It is the object of the present invention to provide a method and an apparatus for producing foil bags, wherein the manufacture of corresponding recesses is checked in a reliable manner.
During the supply operation, holes are at least punched into the bottom foil, the holes being spaced apart in the running direction of the bottom foil at a distance corresponding to the width of one foil bag. These holes are substantially arranged in symmetry with the center line of the bottom foil in the running direction. The bottom foil is folded along said center line. The punching operation and the folding operation can also be interchanged. During the supply operation a measuring operation is carried out after the punching operation for determining whether punched holes have been produced. The side foils and the folded bottom foil are placed one upon the other and are connected at the future side edges of the foil bag such that at the place where the bottom foil is positioned between the side foils the side edges are only directly interconnected by the punched holes. Finally, the connected foil sequence is cut such that the side-edge connecting area is respectively divided between two foil bags.
Hence, in the method according to the invention, it is already checked before the introduction of the bottom foil whether the punched holes have been provided at all and whether they have been introduced in the correct position and at the correct distance.
The optical measurement can be employed in the further course of the process, for example, for transmitting an acoustic or optical alarm signal to the operating personnel or for stopping the foil-bag producing device. Since the punched holes are already detected prior to the introduction of the bottom foil between the side foils, defective foil bags that would have to be sorted out at a later time are not produced. Thus, the method according to the invention enhances the reliability and avoids time losses caused by malfunctions.
In the method according to the invention the punching operation can be carried out prior to the folding operation for the bottom foil. For instance, the presence of punched holes can be checked individually and exactly for all punched holes that are arranged side by side in a direction perpendicular to the running direction of the bottom foil. However, it is just as well possible that the folding operation is carried out prior to the punching operation. The punching operation and the hole measuring operation can thus be carried out in an efficient manner and with a minimum number of punching and measuring means.
The foils can be adhesively bonded to one another along the future edges. However, sealed or welded edges are very simple and reliable.
The measurement as to whether the punched holes have been produced can e.g. be carried out with the help of corresponding contact sensors. An optical measurement, however, is advantageously provided for. An optical measurement guarantees a highly reliable contactless measuring operation.
Another advantageous development provides for proximity switches which can be used in the case of metal-containing foils and are less prone to soiling and moisture.
The punched holes are symmetrically arranged around the center line of the bottom foil at which the bottom foil is folded. A single punched hole may here be provided in a direction perpendicular to the running direction of the bottom foil, said single hole being folded at the same time when the bottom foil is folded. However, the reliability of the production process and the stability of the foil bag are enhanced when two respective punched holes are provided in a direction perpendicular to the running direction of the bottom foil, the holes being superimposed by the folding operation.
In an advantageous development of the method a measurement is carried out before the foils are connected to determine whether a bottom foil has been supplied at all. A malfunction of the supply mechanism of the bottom foil can thus be detected in an easy manner, and side foils can be prevented from being interconnected without a bottom foil being positioned thereinbetween. Moreover, a tom foil or the end of the foil can also be determined in this manner.
Finally, the sensor can also be used for detecting the time when a malfunction, such as a tom foil, occurs between the sensor and a processing station which is arranged downstream thereof. Such a malfunction is detected in that the signal state of the sensor does not change.
Advantageously, such a measurement is again carried out in an optical manner, which is made possible by contactless detection or with the help of a proximity switch. In a simple development of the method according to the invention, the hole measurement for detecting whether punched holes are present and the foil measurement for detecting whether a bottom foil has been supplied are carried out with the aid of a joint measurement device.
The method according to the invention can be carried out in a highly efficient manner when the two supplied side foils have each a width corresponding to that of the extension of a plurality of foil bags and when a corresponding number of bottom foils are supplied. It is thus possible to produce a plurality of foil bags side by side, and individual components, such as the connecting means or the cutting means for cutting the foils into individual bottom foils, need only be provided once.
The foil-bag producing apparatus of the invention for carrying out the method according to the invention comprises a punching means for punching holes into the bottom foil that are arranged in symmetry with the center line of the bottom foil, as well as a measuring means for detecting the punched holes. A second measuring means may advantageously be provided for detecting whether a bottom foil exists.
An advantageous embodiment comprises a light barrier as a measuring point. The signal of a light barrier can be read out in an easy manner and can be used for directly producing an alarm signal or for switching off the apparatus.
Another advantageous embodiment comprises a proximity switch as a measuring point. Such a proximity switch is less prone to soiling and moisture and can specifically be used in metal-containing foils.